1. Field of the Invention
The present invention relates to a semiconductor laser apparatus capable of emitting a plurality of light beams respectively having different wavelengths and an optical pickup apparatus comprising the same.
2. Description of the Background Art
Conventionally, semiconductor laser devices that emit infrared light beams having wavelengths of approximately 780 nm (infrared semiconductor laser devices) have been used as light sources for compact disk (CD) drives. Further, semiconductor laser devices that emit red light beams having wavelengths of approximately 650 nm as light sources (red semiconductor laser devices) have been used for conventional digital versatile disk (DVD) drives.
On the other hand, DVDs capable of recording and reproduction using blue-violet light beams having wavelengths of approximately 405 nm have been developed in recent years. In order to record and reproduce such DVDs, DVD drives using semiconductor laser devices that emit blue-violet light beams having wavelengths of approximately 405 nm (blue-violet semiconductor laser devices) have been also simultaneously developed. In these DVD drives, compatibilities with conventional CDs and DVDs are required.
In this case, compatibilities with conventional CDs, DVDs, and new DVDs are realized by a method of providing a plurality of optical pickup apparatuses that respectively emit an infrared light beam, a red light beam, and a blue-violet light beam to the DVD drives or a method of providing an infrared semiconductor laser device, a red semiconductor laser device and a blue-violet semiconductor laser device within one optical pickup apparatus. Since the number of components is increased in these methods, however, it is difficult to miniaturize the DVD drives, simplify the configurations, and reduce the costs.
In order to thus prevent the number of components from being increased, semiconductor laser devices in which infrared semiconductor laser devices and red semiconductor laser devices are integrated into one chips have been put to practical use.
Both the infrared semiconductor laser devices and the red semiconductor laser devices can be integrated into one chips because they are formed on GaAs substrates. On the other hand, the blue-violet semiconductor laser devices are not formed on GaAs substrates, so that it is significantly difficult to integrate both the blue-violet semiconductor laser devices, together with the infrared semiconductor laser devices and the red the semiconductor laser devices, into one chips.
Therefore, a light emitting apparatus having a configuration in which an infrared semiconductor laser device and a red semiconductor laser device are formed on the same chip to manufacture a monolithic red/infrared semiconductor laser device, a blue-violet semiconductor laser device is formed into separate chips, and the chips of the blue-violet semiconductor laser device and the chips of the monolithic red/infrared semiconductor laser device are stacked has been proposed (see JP 2001-230502 A, for example).
In a case where the light emitting apparatus is mounted within an optical pickup apparatus, spaces respectively occupied by the blue-violet semiconductor laser device, the infrared semiconductor laser device, and the red semiconductor laser device in the optical pickup apparatus are reduced.
In the above-mentioned light emitting apparatus, respective emission points of the semiconductor laser devices are spaced apart from one another. Consequently, it is preferable that the optical pickup apparatus containing the plurality of semiconductor laser devices is provided with an optical system and a photodetector corresponding to each of the semiconductor laser devices. In this case, it is possible to accurately introduce light beams emitted from the plurality of semiconductor laser devices into the optical recording medium as well as to accurately introduce light beams reflected from the optical recording medium into the light receiving device. When the optical pickup apparatus is provided with the optical system and the photodetector corresponding to each of the semiconductor laser devices, however, the size of the optical pickup apparatus is increased.
In JP 2001-230502 A, an example in which a light emitting apparatus comprising a blue-violet semiconductor laser device, an infrared semiconductor laser device, and a red semiconductor laser device is mounted within an optical disk recording/reproducing apparatus provided with an optical system and a photodetector that are common among the three semiconductor laser devices is illustrated.
However, optical paths of laser beams respectively emitted from the blue-violet semiconductor laser device, the red semiconductor laser device, and the infrared semiconductor laser device do not coincide with one another. In order to carry out accurate signal reproduction, tracking control, focus control, and tilt control, therefore, an optical disk recording/reproducing apparatus must be actually provided with three photodetectors respectively corresponding to three laser beams. Consequently, it is difficult to miniaturize the optical disk recording/reproducing apparatus.